PDF Publication Title:
Text from PDF Page: 006
Paper Journal of Materials Chemistry A Fig. 3 (a) Digital images of the volume changes of AC, AC-CO2, AC@S and AC/S-155. (b) XRD spectra of the AC, AC-CO2, AC@S and AC/S-155 composites and sublimed sulfur. Inset is an enlarged view. (c) Raman spectra of AC, AC-CO2, AC@S and AC/S-155. (d) TG curves of pure sulfur, AC@S and AC/S-155. (e) N2 adsorption–desorption isotherm curves for AC, AC-CO2 and AC@S. View Article Online respectively, implying that sulfur was successfully incorporated into the carbon matrices. Combined with the aforementioned TEM results, the corresponding expansion mechanism can be described as follows. SC-CO2 as a nonpolar solvent has a powerful dissolving capability, and can easily dissolve nonpolar sulfur powder at the molecular level.48 Therefore, CO2 molecules and sulfur molecules carried by SC-CO2 can pene- trate into graphitic layers and pores of carbon matrices and remain as stable species during the initial stage of the SC-CO2 process. When exposed to an abrupt decrease in pressure, the intercalated CO2 molecules immediately transform into CO2 gas, which creates a large pressure difference between graphitic layers/inner pores and the ambient environment. This large pressure difference can generate enough force to peel off graphitic sheets along the c-axis direction or greatly weaken the van der Waals interplanar interactions of carbon matrices. Meanwhile, the dissolved sulfur remains at the interlayers or pores of carbon matrices when SC-CO2 uid transforms to CO2 gas. As a result, the SC-CO2 process will not only enlarge the interlayer spacings or pores of carbon materials, but also may exfoliate graphite into small graphitic sheets to further increase the specic surface area and volume of carbon materials. More importantly, these expanded interlayer spacings, pores and increased specic surface area will be favorable for impreg- nating sulfur and trapping polysuldes, which may greatly enhance the electrochemical performance in Li–S batteries. The phase structures of AC, AC-CO2, AC@S and AC/S-155 samples are further analyzed by XRD. As shown in Fig. 3b, AC and AC-CO2 samples have two broad diffraction peaks at around 23 and 45, indicating that the SC-CO2 process does not alter the amorphous structure of the AC sample. Aer impregnating sulfur into the AC matrices with the assistance of SC-CO2 uid, the XRD pattern of AC@S was similar to AC and AC-CO2 samples, and no obvious sulfur peaks were detected in the AC@S sample. It is worth noting that aer SC-CO2 treatment the phase structure of the pristine sulfur does not change, and it retains good crystallinity as shown in Fig. S6.† The above results demonstrate that sulfur is completely encapsulated within the interlayers and pores of AC matrices with a uniform distribu- tion. In contrast, the well-dened diffraction peaks of crystal- line S8 exist in the AC/S-155 sample, revealing that there are large numbers of sulfur particles still on the surface of the AC matrices. This result also conrms that the SC-CO2 method is more effective than the thermal diffusion method for achieving the highly homogeneous distribution of sulfur in carbon matrices. Additionally, due to the graphitic structure of MCMB, which is quite different from AC, the MCMB and MCMB@S samples were employed to verify the differences in using amorphous carbon and crystalline carbon as sulfur hosts during the SC-CO2 process. As shown in Fig. S7a,† the MCMB sample shows one sharp peak at around 26.5, which belongs to the typical diffraction peak of graphite. Interestingly, this peak shis to a lower angle aer sulfur incorporation via the SC-CO2 treatment. This result vividly proves that the interlayer spacings of MCMB are greatly enlarged during SC-CO2 treatment, matching TEM results (Fig. S3a–d†). Moreover, the diffraction This journal is © The Royal Society of Chemistry 2017 J. Mater. Chem. A Published on 24 November 2017. Downloaded by University of Texas Libraries on 08/12/2017 20:16:36.PDF Image | Supercritical CO2 Mediated Incorporation of Sulfur into Carbon Matrix
PDF Search Title:
Supercritical CO2 Mediated Incorporation of Sulfur into Carbon MatrixOriginal File Name Searched:
SupercriticalCO2mediatedincorporationofsulfurintocarbonmatrixascathodematerialstowardshigh-performancelithiumsulfurbatteries.pdfDIY PDF Search: Google It | Yahoo | Bing
Sulfur Deposition on Carbon Nanofibers using Supercritical CO2 Sulfur Deposition on Carbon Nanofibers using Supercritical CO2. Gamma sulfur also known as mother of pearl sulfur and nacreous sulfur... More Info
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
| CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com | RSS | AMP |